(a) Field of the Invention
The present invention relates to an image forming apparatus and a transfer belt unit, and more particularly to a method of assembling a transfer belt unit of the image forming apparatus.
(b) Discussion of the Related Art
Recently, increased numbers of users have been using a full color printing function of an image forming apparatus, and they have been demanding an image forming apparatus capable of conducting full color imaging processes in a substantially same time required for monochrome imaging processes.
Accordingly, an image forming apparatus of tandem type having a plurality of photoconductive members has been developed to decrease a process time required for full color imaging processes. A typical image forming apparatus of tandem type employs a direct transfer method or an indirect transfer method.
In the direct transfer method, images formed on the each of the photoconductive members are sequentially and directly transferred to a recording sheet transported on a transfer belt unit. In the indirect transfer method, images formed on the each of the photoconductive members are sequentially transferred to an intermediate transfer member (e.g., an intermediate transfer belt) by a primary transfer unit. The images on the intermediate transfer member are then transferred to a recording sheet by a secondary transfer unit en bloc.
Typically, the primary transfer unit includes a frame, a plurality of support rollers, and a belt. The plurality of support rollers is rotatably supported by the frame, and the belt is extended by the plurality of support rollers.
The primary transfer unit is configured to be detachable from an image forming apparatus. By this arrangement, the primary transfer unit can be removed for maintenance and replaced, as required.
The primary transfer unit is detachable from the image forming apparatus by several methods, such as by attaching or detaching the primary transfer unit in an axis direction of the support rollers of the primary transfer unit, or by attaching or detaching the primary transfer unit in a direction perpendicular to an axis direction of the support rollers of the primary transfer unit, for example.
As for a typical image forming apparatus, the primary transfer unit (i.e., transfer belt unit) is detachable in an axis direction of the support rollers, the axis direction of the support rollers coinciding with the front-to-rear direction of the image forming apparatus. Therefore, attachment and detachment of the transfer belt unit to the image forming apparatus can be accomplished at the front side of the image forming apparatus, resulting in a relatively higher efficiency of attachment and detachment.
However, in such a configuration, the image forming apparatus does not have a board supporting one end of the support rollers at the front side of the image forming apparatus, because attachment and detachment of the transfer belt unit is performed from the front side of the image forming apparatus.
Such image forming apparatus can support one end of the support rollers at the rear side of the image forming apparatus, but may not support the other end of the support rollers at the front side of the image forming apparatus. Therefore, the transfer belt unit may not be accurately positioned in the image forming apparatus.
To avoid these problems, some image forming apparatuses support the transfer belt unit at both front and rear sides of the image forming apparatus. In such image forming apparatus, one side of the transfer belt unit is connected to a board at the rear side of the image forming apparatus, and the other side of the transfer belt unit is connected to a board at the front side of the image forming apparatus. Attachment and detachment of the transfer belt unit is performed in an axis direction of the support rollers of the transfer belt unit. Such configuration may increase a positional accuracy of the transfer belt unit in the image forming apparatus.
However, the above-mentioned board is made of a metal sheet having a thickness of 1 mm or more, for example, and typically, such board is not integrated with the transfer belt unit but is a separate component. Therefore, inexperienced users may experience difficulties in attachment and detachment of the transfer belt unit.
To avoid these problems, some transfer belt units are integrated with a board. However, such transfer belt units have increased weights. In addition, such transfer belt units may have increased manufacturing cost because of the integrated board, which is disfavored in the transfer belt unit that will be replaced within a specific period.
Another image forming apparatus uses a transfer belt unit having a belt and support rollers supported by a frame formed from a resinous material, and a unit housing. The unit housing encases the transfer belt unit and is then attached in the image forming apparatus.
However, such configurations are complex, resulting in an increase of manufacturing cost of the transfer belt unit. In addition, attachment and detachment between the transfer belt unit and the unit housing is required when replacing the transfer belt unit. Further, a drive roller included in the support rollers of the transfer belt unit should be securely coupled to a driving system of the image forming apparatus so that the coupling is not disconnected. To do so, an elastic member, such as a spring and/or rubber, is disposed between the board of the image forming apparatus and the transfer belt unit as a force-biasing member to force the transfer belt unit to the image forming apparatus. By this arrangement, disconnection of the drive roller and the driving system of the image forming is prevented. However, the elastic member is provided as separate component, resulting in an increase of the manufacturing cost of the transfer belt unit.